Support / FAQs / About techtown

Home Forums Welcome to techtown Burner Problem

  • Burner Problem

     fixbear updated 5 months, 3 weeks ago 5 Members · 14 Posts
  • Squeeker

    November 10, 2020 at 3:04 pm

    South Bend convection oven MN#GS/25SC . Burners light but wont stay lit. Flame goes out in 5 seconds. Flame floats and isnt steady. i dont want to assume that the flame sensor is bad if the flame is not hot enough to generate a good micro amp signal. I cleaned the burners and also checked the burner manifold. Gas valve checks out ok @ 2.5 inch W.C . But the micro amp reading during ignition was only .2 micro amps. also I by passed the 24 volts from the ignition module and went directly off the transformer after ignition so that I was controlling the gas valve and not the control module and not the flame sensor but still got the same results. The flame would just die down even though 24 volts was still being fed to the gas valve. Is it possible that I have partial blockage in the gas supply piping to the oven. I have 5 in W.C. going to the gas valve but maybe not enough volume of gas flow to the valve .Can you give me any suggestions? Thanks Squeeker.

  • fixbear

    November 10, 2020 at 4:38 pm

    First, do you mean a GS-25SC vs a GS-255C?

    You need to put a manometer on the manifold to monitor the pressure. to the burners. I suspect you have a blocked vent on the valve preventing it from adjusting to the atmospheric pressure.

    But make sure you first check the supply valve to be fully open and if it has a quick couple, that it is fully locked in. This is very common to see after a major cleaning cycle.

  • ShawnF

    November 10, 2020 at 4:42 pm

    2.5 in. wc gas pressure seems a bit low.

  • fixbear

    November 10, 2020 at 4:43 pm

    BTW, it’s supposed to have 4 inches to the manifold. Per South Bend service manual.

    Not 2.5

  • fixbear

    November 10, 2020 at 4:53 pm

    By the way, you never stated whether it was the top oven, bottom oven, or both. If it’s both, look at the supply.

  • fixbear

    November 10, 2020 at 5:14 pm

    Finally found the flame sensor value. This from there install manual.

    Check in series on micro amps. Minimum is 0.75 amps, no maximum

  • olivero

    November 11, 2020 at 3:39 pm

    I’ll agree with the 2.5″, fairly common is 3.5″ and some equipment is more.

    If the flame actually lights and then goes out, your gas valve is obvoisly opening, at which point it could be the flame monitor or control module.

    I have seen gas valves fail to stay open during run time leading to some annoying repairs, if you measure the A draw on the coil that is powered by the 24V it’ll tell you a number most likely below 1, so 0.5 or 0.6 or 0.7 or something like that, the manual or spec sheet for the gas valve should have the info in terms of what it should be. That’s how I eventually started catching these intermittent failure gas valves as the A was just high enough to pull it open but any slight flicker would drop it back down and lock it out.

    If there’s a regulator, sometimes the vent limiter gets plugged and it won’t allow the diapraghm inside to move up and down, essentially locking you into a low gas pressure, if the gas was higher before and is now low, then I would be looking for why that is rather than just turning it up.

    • fixbear

      November 12, 2020 at 5:49 am

      Olivero, His gas pressure is way low as is his sense current. This is a hot surface ignition with a 5 sec try and 3 try’s before lockout. But he has a big aid in that a Capable Controls tells you what is not right with a LED that flashes. It’s a Honeywell system of gas control. It actually tests the gas valve coil. As well as the igniter, supply voltage, and control self test.

      • olivero

        November 12, 2020 at 12:45 pm


        I think correcting the gas pressure would be the first thing, but why is it low all of a sudden?

        It’s not a new install so something obviously changed.

  • fixbear

    November 12, 2020 at 1:31 pm

    exactly my thoughts. But we have no knowledge if it was properly adjust at install. I’d start with that and cleaning the flame sensor. Then check the burner ground circuit for resistance.

    • olivero

      November 12, 2020 at 6:24 pm

      I agree, but if the unit has been working since it was installed and is just now having problems, something’s got to have changed.

      I think a good thorough check of the unit and it’s parameters would reveal the problem.

      Could be something as simple as a bad regulator, if it has one.

  • ectofix

    November 12, 2020 at 6:42 pm

    Nobody has asked or mentioned the gas type supplied to the oven.

    Is the oven set up for natural gas or LP? Incoming PRESSURE to the gas valve is important for each. A minimum of 7″WC for NG or 11″WC for LP incoming pressure to the gas valve is crucial for proper oven operation. For this Southbend oven, the combination valve’s internal regulator should be set from the factory to 4″WC for NG or 11″WC for LP. That’s what the burners should see. 2.5″WC is far too low for NG and ridiculously too low for LP. Is this a new installation, or one which worked fine and then suddenly acted up? I ask that because the diameter of the gas supply line is ALSO crucial to proper operation. If gas supply lines are too small, then the oven is doomed from the start. If this oven is installed on a common line with other equipment, is the MAIN gas line an adequate diameter for supplying ALL line equipment when they’re all operating simultaneously? Is the common (main) gas line supply pressure at 1/2 psi (14″WC) or less? It SHOULD be, since most every type of gas control (combination valves, pilot safety valves, dedicated in-line regulators, etc.) are rated for a MAXIMUM of 1/2 psi. If incoming pressure is higher, then there WILL be problems. If your main IS 1/2 psi or less…and you see a dedicated in-line regulator feeding the oven, get rid of it! The oven’s combination valve already has a regulator, so having an additional in-line regulator serves NO purpose and will become yet ANOTHER source for future problems (like getting grease clogging its vent).

    * * * * * * *

    These are just some basic questions which one should first address about gas cooking equipment problems before getting wrapped up in the more intimate questions about a system’s functional details.

  • ectofix

    November 12, 2020 at 8:05 pm


    @Squeeker never mentioned whether this oven previously worked fine and then acted up. Nor did he state what the specified gas type the oven is set up for and what is supplied.

    Yet – the responses I read here were based upon assumptions made regarding BOTH.

    In practice, we must ask for more details about the questions rolling through here in order to provide proper guidance.

    BTW @ShawnF , when I was in the field, a prerequisite for initially addressing ANY service call required gathering ALL info about equipment problems was to get readings starting from the SOURCE. You probably already do that from your experiences working on generators (as did I) in the military.

    However, folks who work in-house in the civilian sector (like you do in the school system and like I PRESENTLY do where I work) don’t necessarily follow that regime due to our own familiarity of our daily “job site”. That’s an unfortunate practice since we tend to overlook some basics.

    So, when “addressing” ANY cooking equipment, you need to first get the fundamental information:

    Make Model Serial number Rated voltage Actual voltage Rated gas pressure Actual gas pressure Rated amperage Actual amperage Etc.

    You get my drift from there.

    ALSO when I did field service work, annotating ALL of that onto your service call’s work order (per the blocks [fields] provided) was a prerequisite. If the blocks (fields) on the ticket were NOT filled out, then that service call was automatically invalidated for any claims from customers disputing that they shouldn’t be charged for a call back.

    AGAIN, most of our in-house duties don’t require any of that – so such things aren’t a concern and lends to some unfortunate oversight on our part.

  • fixbear

    November 13, 2020 at 5:36 pm

    Ecto, your right. I assumed a bit so I guess I’m a ass. But if it was LP, at 2.5 inches, with the smaller orifices, It wouldn’t have done anything but flash a yellow flame and go out. Exactly why they use propane for all the stunt work. I miss the old South Bend’s with the modulating thermostats. The only convection oven that held within 2 degrees that I ever saw.

Log in to reply.

Original Post
0 of 0 posts June 2018